net: remove delay at device dismantle

I noticed extra one second delay in device dismantle, tracked down to
a call to dst_dev_event() while some call_rcu() are still in RCU queues.

These call_rcu() were posted by rt_free(struct rtable *rt) calls.

We then wait a little (but one second) in netdev_wait_allrefs() before
kicking again NETDEV_UNREGISTER.

As the call_rcu() are now completed, dst_dev_event() can do the needed
device swap on busy dst.

To solve this problem, add a new NETDEV_UNREGISTER_FINAL, called
after a rcu_barrier(), but outside of RTNL lock.

Use NETDEV_UNREGISTER_FINAL with care !

Change dst_dev_event() handler to react to NETDEV_UNREGISTER_FINAL

Also remove NETDEV_UNREGISTER_BATCH, as its not used anymore after
IP cache removal.

With help from Gao feng

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Mahesh Bandewar <maheshb@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

8 files changed, 27 insertions, 24 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4936f09a9333..9ad7fa8c10e0 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1553,7 +1553,7 @@ struct packet_type {
 #define NETDEV_PRE_TYPE_CHANGE  0x000E
 #define NETDEV_POST_TYPE_CHANGE 0x000F
 #define NETDEV_POST_INIT        0x0010
-#define NETDEV_UNREGISTER_BATCH 0x0011
+#define NETDEV_UNREGISTER_FINAL 0x0011
 #define NETDEV_RELEASE          0x0012
 #define NETDEV_NOTIFY_PEERS     0x0013
 #define NETDEV_JOIN             0x0014
diff --git a/net/core/dev.c b/net/core/dev.c
index 088923fe4066..0640d2a859c6 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1406,7 +1406,6 @@ rollback:
                                 nb->notifier_call(nb, NETDEV_DOWN, dev);
                         }
                         nb->notifier_call(nb, NETDEV_UNREGISTER, dev);
-                        nb->notifier_call(nb, NETDEV_UNREGISTER_BATCH, dev);
                 }
         }
 
@@ -1448,7 +1447,6 @@ int unregister_netdevice_notifier(struct notifier_block *nb)
                                 nb->notifier_call(nb, NETDEV_DOWN, dev);
                         }
                         nb->notifier_call(nb, NETDEV_UNREGISTER, dev);
-                        nb->notifier_call(nb, NETDEV_UNREGISTER_BATCH, dev);
                 }
         }
 unlock:
@@ -1468,7 +1466,8 @@ EXPORT_SYMBOL(unregister_netdevice_notifier);
 
 int call_netdevice_notifiers(unsigned long val, struct net_device *dev)
 {
-        ASSERT_RTNL();
+        if (val != NETDEV_UNREGISTER_FINAL)
+                ASSERT_RTNL();
         return raw_notifier_call_chain(&netdev_chain, val, dev);
 }
 EXPORT_SYMBOL(call_netdevice_notifiers);
@@ -5331,10 +5330,6 @@ static void rollback_registered_many(struct list_head *head)
                 netdev_unregister_kobject(dev);
         }
 
-        /* Process any work delayed until the end of the batch */
-        dev = list_first_entry(head, struct net_device, unreg_list);
-        call_netdevice_notifiers(NETDEV_UNREGISTER_BATCH, dev);
-
         synchronize_net();
 
         list_for_each_entry(dev, head, unreg_list)
@@ -5787,9 +5782,8 @@ static void netdev_wait_allrefs(struct net_device *dev)
 
                         /* Rebroadcast unregister notification */
                         call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
-                        /* don't resend NETDEV_UNREGISTER_BATCH, _BATCH users
-                         * should have already handle it the first time */
-
+                        rcu_barrier();
+                        call_netdevice_notifiers(NETDEV_UNREGISTER_FINAL, dev);
                         if (test_bit(__LINK_STATE_LINKWATCH_PENDING,
                                      &dev->state)) {
                                 /* We must not have linkwatch events
@@ -5851,9 +5845,8 @@ void netdev_run_todo(void)
 
         __rtnl_unlock();
 
-        /* Wait for rcu callbacks to finish before attempting to drain
-         * the device list.  This usually avoids a 250ms wait.
-         */
+
+        /* Wait for rcu callbacks to finish before next phase */
         if (!list_empty(&list))
                 rcu_barrier();
 
@@ -5862,6 +5855,8 @@ void netdev_run_todo(void)
                         = list_first_entry(&list, struct net_device, todo_list);
                 list_del(&dev->todo_list);
 
+                call_netdevice_notifiers(NETDEV_UNREGISTER_FINAL, dev);
+
                 if (unlikely(dev->reg_state != NETREG_UNREGISTERING)) {
                         pr_err("network todo '%s' but state %d\n",
                                dev->name, dev->reg_state);
@@ -6256,7 +6251,6 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
            the device is just moving and can keep their slaves up.
         */
         call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
-        call_netdevice_notifiers(NETDEV_UNREGISTER_BATCH, dev);
         rtmsg_ifinfo(RTM_DELLINK, dev, ~0U);
 
         /*
diff --git a/net/core/dst.c b/net/core/dst.c
index 56d63612e1e4..f6593d238e9a 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -374,7 +374,7 @@ static int dst_dev_event(struct notifier_block *this, unsigned long event,
         struct dst_entry *dst, *last = NULL;
 
         switch (event) {
-        case NETDEV_UNREGISTER:
+        case NETDEV_UNREGISTER_FINAL:
         case NETDEV_DOWN:
                 mutex_lock(&dst_gc_mutex);
                 for (dst = dst_busy_list; dst; dst = dst->next) {
diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index ab7db83236c9..585093755c23 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -711,15 +711,16 @@ static int fib_rules_event(struct notifier_block *this, unsigned long event,
         struct net *net = dev_net(dev);
         struct fib_rules_ops *ops;
 
-        ASSERT_RTNL();
 
         switch (event) {
         case NETDEV_REGISTER:
+                ASSERT_RTNL();
                 list_for_each_entry(ops, &net->rules_ops, list)
                         attach_rules(&ops->rules_list, dev);
                 break;
 
         case NETDEV_UNREGISTER:
+                ASSERT_RTNL();
                 list_for_each_entry(ops, &net->rules_ops, list)
                         detach_rules(&ops->rules_list, dev);
                 break;
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 34d975b0f277..c64efcff8078 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2358,7 +2358,7 @@ static int rtnetlink_event(struct notifier_block *this, unsigned long event, voi
         case NETDEV_PRE_TYPE_CHANGE:
         case NETDEV_GOING_DOWN:
         case NETDEV_UNREGISTER:
-        case NETDEV_UNREGISTER_BATCH:
+        case NETDEV_UNREGISTER_FINAL:
         case NETDEV_RELEASE:
         case NETDEV_JOIN:
                 break;
diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index adf273f8ad2e..6a5e6e4b142c 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1147,8 +1147,12 @@ static int inetdev_event(struct notifier_block *this, unsigned long event,
                          void *ptr)
 {
         struct net_device *dev = ptr;
-        struct in_device *in_dev = __in_dev_get_rtnl(dev);
+        struct in_device *in_dev;
 
+        if (event == NETDEV_UNREGISTER_FINAL)
+                goto out;
+
+        in_dev = __in_dev_get_rtnl(dev);
         ASSERT_RTNL();
 
         if (!in_dev) {
diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_fronten